"It's very difficult to bring ambience and environmental character to what is basically an urban motorway," said NHIG founder John Scott.

"We looked at it and thought: 'What can we do here to this awful mess?'"

Starting with the public lavatories on Westbourne Grove, now with a built-in florist, the group already has several major projects under its belt.

A mosaic by school children has given a former "muggers' alley" off Kensington Church Street a new lease of life and a moving wind sculpture, The Climber, clings to the top of David Game House on Notting Hill Gate.

Just down the road, the spinning eyes of a 10ft stainless steel Carnival Elephant by artist Nadim Karam have been keeping watch and attracting admiring glances outside Waterstones since August 2003.

Now the group is trying to get its most eye-catching project yet off the ground - two glowing "eco halos" suspended over Notting Hill Gate.

Low-energy red, blue and green LEDs would be encased in two polycarbonate rings sculpted by artist Dante Leonelli and would change in response to their environment.

I think art can revive an area, it can lift people's spirits and give it a sense of place

John Scott, NHIG

Hooked up to monitoring equipment already in place, they would reflect air pollution levels - changing through the spectrum from white to red and raise awareness.

"They will define the centre of Notting Hill Gate, which is in between the two halos," said Mr Scott.

Air quality analyst Ben Barratt, from King's College, said inner London suffered from between 40 and 50 days of "moderate" air pollution in summer - about six in winter - but never reached the "very high" rating.

"It looks like traffic emissions are going down, traffic levels in London are stabilising and going down slowly, but ozone levels are increasing slightly - it depends on the length of the summer," he said.

"It's driven by the weather. Athens has day after day of smog, if we didn't have the traditional English weather things would be a lot worse."

Notting Hill Gate is split by six lanes of traffic

If the pollution does not bring a technicolour display to Notting Hill Gate, the rings can be switched to respond to other stimuli such as noise or heat.

The idea is to bring "a sense of harmony and identity to this well-known but ignored public place", according to architect Philip Gumuchdjian.

After some concerns that Notting Hill residents would be running for cover when the halos turn red - indicating high pollution - the council granted the project planning permission last year.

The group is now working on finding a backer to provide £1m and said it had had "some interest", but it was proving difficult to pin a sponsor down.

"It's very difficult to raise £1m and we haven't been able to do it yet," said Mr Scott, who, after three years working on the project, is determined to see it through.

"I think art can revive an area, it can lift people's spirits and give it a sense of place," he said.